This invention relates to halogen-containing resin lens materials, more particularly to a halogen-containing resin lens material having high refractive index and low dispersion.
In the prior art, various inorganic glass lenses have been employed for optical instruments. In recent years, however, synthetic resin lenses are beginning to be widely used together with inorganic glass lenses for their light weight, workability, dyeing property, adaptability to quantity production, and possibility of low cost.
Among the various physical properties required of a lens, a high refractive index and a low dispersion are very important. Possession of a high refractive index not only makes the lens system constituting an important part in optical instruments such as microscope, camera, telescope, etc., or in spectacle lens compact and light in weight, but also has the advantage of reducing spherical aberrations etc. On the other hand, low dispersion is very important as a matter of course for reducing chromatic aberration. A characteristic which is difficult to realize in an inorganic glass lens is the property of being dyeable with dyes of various colors, and this property is an indispensable property of a synthetic resin lens. In particular, it is most preferable that the lens can be dyed as such to a desired color.
However, even in synthetic resin lenses in general, lenses with higher refractive index tend to have higher dispersion, while those with lower refractive index tend to have lower dispersion, similarly as in the case of inorganic glasses. For example, a currently available lens material most popularly used for organic lenses for spectacles in diethylene glycol bisallylcarbonate (hereinafter referred to as CR-39). Although CR-39 has a high Abbe number of .nu.=60 (i.e., low dispersion), its refractive index is very low, being n.sub.D.sup.20 =1.50. Polymethyl methacrylate, which is sometimes used as lens material, also has a high Abbe number of .nu.=60 similarly as CR-39, but its refractive index is as low as n.sub.D =1.49. Polystyrene (n.sub.D =1.59, .nu.=30.4) and polycarbonate (n.sub.D =1.59, .nu.=29.5), which are said to have a relatively high refractive index and a low dispersion, have been pointed out to be deficient in other physical properties required for a lens material such as surface hardness, solvent resistance and dyeability property. Polynaphthyl methacrylate (n.sub.D =1.64) and Polyvinyl naphthalene (n.sub.D =1.68) having high refractive index have low Abbe numbers of .nu.=24 and .nu.=20, respectively. Thus, many problems accompany all of these materials.
Recently, it has been proposed to use a halogen-substituted phenyl ester of methacrylic acid or a halogen-substituted bisphenol-A derivative for a plastic lens material in order to obtain a high refractive index, as disclosed in Japanese Laid-open Patent Publication Nos. 15118/1980, 13747/1980, 28117/1983 and 54901/1982. However, the copolymers disclosed in these Publications are characterized by having high refractive indices, but nothing is said about dyeability property and Abbe number. As for dyeability property, CR-39 has good dyeable property but has low refractive index as described above. Generally speaking, for enhancement of refractive index, compounds having aromatic groups such as phenyl group, naphthyl group, etc. or compounds having halogenic groups are used. Unfortunately, however, these groups are strongly hydrophobic and generally tend to lower the dyeability property.
Thus, there has been a demand for a plastic lens material having a high refractive index, low dispersion, dyeability property, solvent resistance, and other desirable characteristics.